Field of the Invention
This invention relates to a communication verification system, and in particular, it relates to a communication verification system useful for extending the transmission distance of communication devices.
Description of the Related Art
Protection of digital data has been an important topic given the advancement of digital technologies. To ensure that digital audio-visual data is not illegally duplicated when transmitted through communication interfaces, developers often add protection mechanisms at the transmitting end, and the corresponding receiving end requires corresponding decoding mechanisms in order to read and display the data content.
Take High-Bandwidth Digital Content Protection (HDCP) technology, a digital content protection technology developed by Intel, as an example, before and during digital audio-visual data transmission, the HDCP transmitting unit performs verification for the connected HDCP receiving unit, to ensure that the HDCP receiving unit is authorized.
Specifically, under the HDCP technology, two computing modes are defined for the HDCP transmitting units to perform verification. Under one computing mode (the first computing mode), the HDCP transmitting unit first transmits an initial value, and after the HDCP receiving unit replies with a confirmation signal, the HDCP transmitting unit transmits a query signal to request the HDCP receiving unit to transmit the computation result. Under the other computing mode (the second computing mode), the HDCP transmitting unit first transmits an initial value, and the HDCP receiving unit immediately transmits back the computation result. Under the first computing mode, the HDCP transmitting unit determines whether the elapsed time from when it transmits the query signal to when it receives the computation result satisfies a predetermined time limitation (for example, under 7 ms), and confirms the correctness of the computation result. Under the second computing mode, the HDCP transmitting unit determines whether the elapsed time from when it transmits the initial value to when it receives the computation result satisfies a predetermined time limitation, and confirms the correctness of the computation result. If the elapsed time for receiving the computation result from the HDCP receiving unit exceeds the time limitation, that HDCP receiving unit will be deemed unauthorized. However, while an HDCP receiving unit constructed according to these computing modes can satisfy the above described time limitations, the transmission distance between the HDCP transmitting unit and the HDCP receiving unit is limited for this reason and cannot be extended. Thus, for data transmission between the HDCP transmitting unit and the HDCP receiving unit, a solution is needed to effectively extend the transmission range while satisfying the time limitation.